linux-kernel - Re: [PATCH v3 17/33] drm/vkms: Introduce config for plane format

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Message-Id: <DFBFLLKWYFB5.23TQQWRA5MD4A@bootlin.com>
Date: Tue, 30 Dec 2025 10:08:15 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Louis Chauvet" <louis.chauvet@...tlin.com>, "Haneen Mohammed"
 <hamohammed.sa@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Melissa Wen"
 <melissa.srw@...il.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "David Airlie"
 <airlied@...il.com>, <jose.exposito89@...il.com>, "Jonathan Corbet"
 <corbet@....net>
Cc: <victoria@...tem76.com>, <sebastian.wick@...hat.com>,
 <thomas.petazzoni@...tlin.com>, <dri-devel@...ts.freedesktop.org>,
 <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v3 17/33] drm/vkms: Introduce config for plane format

Hi Louis,

On Mon Dec 29, 2025 at 4:29 PM CET, Louis Chauvet wrote:
>>> --- a/drivers/gpu/drm/vkms/vkms_config.c
>>> +++ b/drivers/gpu/drm/vkms/vkms_config.c
>>
>>> +void vkms_config_plane_remove_all_formats(struct vkms_config_plane *plane_cfg)
>>> +{
>>> +	plane_cfg->supported_formats_count = 0;
>>
>> Why not kfree(plane_cfg->supported_formats) too? You will be (re)allocating
>> anyway if adding one or all formats later on, so the buffer you're not
>> freeing won't be reused anyway.
>
> IIRC realloc reuse the existing allocated buffer if it is big enough to fit the new
> size. But I think this is probably an oversight here and I will add the free to clarify the situation :-)

Thanks. My point is that keeping the buffer allocated for future use is not
great because if it is not reused it will take memory for all the remaining
uptime.

>>> +}
>>> +
>>> +void vkms_config_plane_remove_format(struct vkms_config_plane *plane_cfg, u32 drm_format)
>>> +{
>>> +	for (unsigned int i = 0; i < plane_cfg->supported_formats_count; i++) {
>>> +		if (plane_cfg->supported_formats[i] == drm_format) {
>>> +			plane_cfg->supported_formats[i] = plane_cfg->supported_formats[plane_cfg->supported_formats_count - 1];
>>
>> I doubt these are less than 100 chars. ;-)
>
> yes, 127, but I don't know how to format it so it is readable.
>
> I tried
>
> plane_cfg->supported_formats[i] =
> 	plane_cfg->supported_formats[plane_cfg->supported_formats_count - 1];
>
> But the second line is 101 chars...

I vote for this one. 101 is close enough to 100, and I see no reaonable way
to format better (and I agree the two below are ugly).

> Checkpatch don't complain if I do:
>
> plane_cfg->supported_formats[i] =
> 	plane_cfg->supported_formats[
> 		plane_cfg->supported_formats_count - 1];
>
> or
>
> plane_cfg->supported_formats[i] =
> 	plane_cfg->supported_formats[plane_cfg->supported_formats_count-
> 		1];
>
> But that very ugly and not readable...

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com